Phase 7: MCP handler (25 tests), NIP-04 encrypt/decrypt (15 tests), CVM server skeleton

- mcp_handler.c/h: 4 tools (get_config, set_config, get_balance, wallet_send)
- nip04.c/h: AES-256-CBC + ECDH with 0x02 compressed pubkey prefix
  - Fixed IV copy bug: mbedTLS AES-CBC modifies IV in-place
  - Base64 encode/decode for ciphertext transport
  - PKCS7 padding
- cvm_server.c/h: Nostr DM listener with FreeRTOS task
- config: cvm_enabled, cvm_relays fields
- 156 total tests passing across 10 test binaries

1 files changed, 10 insertions, 0 deletions

diff --git a/tests/unit/stubs/esp_system.h b/tests/unit/stubs/esp_system.h
index 8e63c80..cd54743 100644
--- a/tests/unit/stubs/esp_system.h
+++ b/tests/unit/stubs/esp_system.h
@@ -1,4 +1,14 @@
 #ifndef STUBS_ESP_SYSTEM_H
 #define STUBS_ESP_SYSTEM_H
 
+#include <stdlib.h>
+#include <stdint.h>
+
+static inline void esp_fill_random(uint8_t *buf, size_t len)
+{
+    for (size_t i = 0; i < len; i++) {
+        buf[i] = (uint8_t)(rand() & 0xFF);
+    }
+}
+
 #endif